1. Field of the Invention
The present invention relates to a waveform equalizer in a recorded information reproduction device for reproducing recorded information from recording media.
2. Description of Related Art
Known is a technique of waveform equalization for improving the S/N ratio of a read signal read from a recording medium on which digital data is recorded at high densities, by performing filtering for strengthening high frequency enhancement on such a read signal. With this technique, the stronger the enhancement of high frequencies of the read signal, the more the S/N ratio can be improved. However, if the high frequencies are strengthened excessively, it will cause an increase in inter symbol interference. To cope with this problem, a waveform equalizer, that can perform high frequency enhancement without causing an increase in inter symbol interference is suggested in Japanese Patent Kokai No. H11-259985.
In such a waveform equalizer, however, a problem exists that a value at the zero-cross point of the read sample value sequence after equalization correction varies when the shortest run length of a read signal is short and thus inter symbol interference is increased, thereby high frequency regions cannot be sufficiently strengthened.
The present invention has been developed in order to solve such a problem. An object of the present invention is to provide a waveform equalizer which can strengthen the high frequency enhancement of the read signal without causing an increase in inter symbol interference even when the shortest run length of the read signal is, for example, not greater than twice the clock period of the channel clock signal.
A waveform equalizer according to the present invention is to perform waveform equalization on a read signal obtained by reading information signals stored in a recording medium, to obtain an equalization corrected read signal, the waveform equalizer comprising amplitude limiting means for limiting the read signal with predetermined amplitude limited values in order to obtain a amplitude limited read signal, a filter for respectively weighting a signal level of the amplitude limited read signal at a first point of time and a signal level of the amplitude limited read signal at a second opint of time, adding the weighted signal levels and outputing a filter output signal, and a summing means for obtaining the equalization corrected read signal by adding a sigal level of the read signal at an intermediate timing of the first and second points of time and the filter output signal.